This application is related to my co-pending application entitled "Real Time Analog Doppler Processor for Weather Radar," Ser. No. 612,385, having the same filing date as this application.
This invention relates to the detection and measurement of atmospheric turbulence and in particular to an analog technique for processing and using the information obtained from small Doppler shifts in the frequency of pulsed radar return signals from precipitation targets to provide an indication of turbulence.
The detection and measurement of atmospheric turbulence has application in meteorology and aviation. In the field of meteorology the study of turbulence and its associated effect on general weather conditions leads to a more accurate and complete form of weather patterns. More importantly, however, the study of atmospheric turbulence is of great concern in the field of aviation because aircraft must be properly apprised of and avoid any hazardous turbulence. Although clear air turbulence is often difficult to measure, reflected radar returns from rain, snow, hail and ice are now capable of providing an indication of the turbulence in the general location of such precipitation in accordance with the teachings of this invention. Moreover, if the radar is sensitive enough to detect the refractive index gradients in clear air turbulence, the technology presented herein is also capable of detection of such turbulence even though precipitation is not present.
The pulsed radar return from precipitation targets are in the nature of a complex waveform having rapid fluctuation in amplitude and phase. The fluctuation rates are usually limited only by the pulse width or the bandwidth of the receiver. The complex nature of the signal represents the vector summation of the simultaneous returns from the plurality of scatters in the radar pulse volume. The size, spatial position and velocity of the precipitation relative to the radar contributes to the nature of the received signal. This affects the instantaneous and average intensity and mean frequency as well as the statistical properties of these parameters. Doppler radar in conjunction with the real analogue Doppler processor of my co-pending application provide for a suitable technique for measuring relative motion between precipitation targets and the source of the radar. As stated in my co-pending application, the velocity of this precipitation is an indirect measurement of the movement of the winds. I have devised a simple method of obtaining turbulence information from the velocity measurement.
Until now there have been significant drawbacks for the use of Doppler radar to provide turbulence information. Among them are the difficulty in making quick and accurate velocity measurements. For example, methods of the prior art require measurements to be made on a large number of samples to be taken of the return signal at each radar range to acquire velocity information. Such techniques use various circuits to provide a sinusoidal estimate of the mean Doppler frequency which is indicative of the precipitation velocity. To obtain this desired result covering many ranges, large scale digital computers or complex data processors capable of storing many samples are employed and then are used to perform a complex mathematical analysis of the values to obtain velocity dependent characteristics. This must be done for each range and as a result the number of calculations is large. Moreover, since turbulence may be viewed as a first derivative of the velocity, the processing circuits must be capable of changing the velocity information into turbulence information. Because of the complexity and difficulty of obtaining velocity information, turbulence detection has often been slow, and any acquired data has been usually meaningless in a fast moving storm situation.
Considering the above drawbacks to the prior art, I have devised a method of providing an instantaneous measurement and remote detection of atmospheric turbulence within precipitation using radar.
It is therefore an object of this invention to provide a simple dicrete system for the instantaneous and continuous measurement of turbulence.
Another object of this invention is to provide a simple delay line circuit in conjunction with a real time analog Doppler processor to provide turbulence information at a given radar range.
And yet a further object of this invention is to provide a warning system for aircraft so that turbulence exceeding a preset level at wavelengths critical to the aircraft is quickly relayed to the pilot.
And yet another object of this invention is to provide a turbulence detection system which is capable of adjustment so that one may select turbulence wavelengths.
Still a further object of this invention is to provide a turbulence measurement with high speed that is useful with a rapid scanning antenna and in such rapidly changing meteorological situations as high speed jet aircraft.